In a typical deployment of a cellular wireless communication network there may be a large variation of required spatial distribution of service coverage and capacity.
Mobility is a basic feature of cellular networks and basic coverage of service is required (almost) everywhere, which is typically achieved by application of a layer of macro cells supported by wide area coverage base station sites.
Suburban and urban areas may require high data throughput and/or accommodation of a large number of users (particularly so in densely populated areas, busy office areas, malls, sports arenas and the like) while rural areas may not. One deployment solution to handle this diversity situation is to introduce one or more layers (not necessarily contiguous) of low power, small coverage cells underlying the macro cell layer. The underlying cells are typically termed micro, pico, or femto cells and create, together with the macro cells, a heterogeneous network (hetnet).
FIG. 1 schematically illustrates a hetnet deployment with two wide area coverage base station sites 131, 132 serving respective macro cells 141, 142, and two small area coverage nodes 111, 112 serving respective pico cells 121, 122. The coverage areas of base stations and pico nodes typically correspond to an output power used by the respective transmitter. FIG. 1 also illustrates two wireless communication devices (hereinafter also referred to as devices) 101 and 102. The wireless communication device 101 is in the coverage area 141 of the base station 131 and also in the coverage area 121 of the pico node 111. Similarly, the wireless communication device 102 is in the coverage area 141 of the base station 131, in the coverage area 142 of the base station 132 and also in the coverage area 122 of the pico node 112.
If the device 101 is receiving a desired signal from the pico node 111, a signal transmitted from the base station 131 and occupying at least part of the frequency region used to transmit the desired signal may be interfering with the reception of the desired signal. Likewise, if the device 101 is receiving a desired signal from the base station 131, a signal transmitted from the pico node 111 and occupying at least part of the frequency region used to transmit the desired signal may be interfering with the reception of the desired signal.
If the device 102 is receiving a desired signal from the pico node 112, a signal transmitted from the base station 131 (and even more so a signal transmitted from the base station 132) and occupying at least part of the frequency region used to transmit the desired signal may be interfering with the reception of the desired signal. Likewise, if the device 102 is receiving a desired signal from the base station 132, a signal transmitted from the pico node 112 and occupying at least part of the frequency region used to transmit the desired signal may be interfering with the reception of the desired signal.
In a typical hetnet deployment the underlying cells may utilize all—or at least a large part of—the available spectrum resources of the cellular communication system to achieve the requirements (e.g. high peak data rate, high user capacity, etc.), while the macro cells may need to use only a smaller part of the available spectrum resources (e.g. based on frequency reuse) to accommodate its commitments (e.g. coverage, mobility) since the underlying layers offload the macro cells.
FIG. 2 schematically illustrates a few example frequency scenarios that may arise in a hetnet deployment.
Part (a) of FIG. 2 illustrates a first situation, where a device (e.g. device 101 of FIG. 1) is receiving a desired signal 214 transmitted from a network node (e.g. pico node 111 of FIG. 1) using carrier frequency f0 and a large signal bandwidth (e.g. 10 MHz) resulting in the frequency region 210. The device also experiences an interfering signal 215 transmitted from another network node (e.g. macro node 131 of FIG. 1) using carrier frequency f1 and a smaller signal bandwidth (e.g. 5 MHz) resulting in the frequency region 212 which is a sub-region of the frequency region 210. No interfering signal is present in the frequency region 211 which is also a sub-region of the frequency region 210.
Part (b) of FIG. 2 illustrates a second situation, where a device (e.g. device 102 of FIG. 1) is receiving a desired signal 224 transmitted from a network node (e.g. pico node 112 of FIG. 1) using carrier frequency f0 and a large signal bandwidth (e.g. 10 MHz) resulting in the frequency region 220. The device also experiences an interfering signal 225 transmitted from another network node (e.g. macro node 131 of FIG. 1) using carrier frequency f1 and a smaller signal bandwidth (e.g. 5 MHz) resulting in the frequency region 222 which is a sub-region of the frequency region 220, and an interfering signal 226 transmitted from yet another network node (e.g. macro node 132 of FIG. 1) using carrier frequency f2 and the smaller signal bandwidth (e.g. 5 MHz) resulting in the frequency region 221 which is also a sub-region of the frequency region 220.
Part (c) of FIG. 2 illustrates a third situation, where a device is receiving a desired signal 234 transmitted from a network node using carrier frequency f0 and a large signal bandwidth (e.g. 15 MHz) resulting in the frequency region 230. The device also experiences an interfering signal 235 transmitted from another network node using carrier frequency f1 and a smaller signal bandwidth (e.g. 5 MHz) resulting in the frequency region 233 which is a sub-region of the frequency region 230, and an interfering signal 236 transmitted from yet another network node using carrier frequency f2 and the smaller signal bandwidth (e.g. 5 MHz) resulting in the frequency region 231 which is also a sub-region of the frequency region 230. No interfering signal is present in the frequency region 232 which is also a sub-region of the frequency region 230.
Thus, due to the use of these multiple layers using more or less overlapping parts of the spectrum and depending on the position of the device, the interference scenario of a device may be very different in different frequency regions of reception. For example, some devices only experience other cell interference in one frequency region of the receiving spectrum (compare with part (a) of FIG. 2), some devices experience other cell interference in all frequency regions of the receiving spectrum, possibly with different power and/or different other characteristics for the respective frequency regions, (compare with part (b) of FIG. 2), some devices experience other cell interference in several—but not all—frequency regions of the receiving spectrum, possibly with different power and/or different other characteristics for the respective frequency regions, (compare with part (c) of FIG. 2) and some devices may not experience any significant interference at all. This type of diversified interference within the same (non-carrier aggregation) reception spectrum is different from typical prior art situations where all pairs of cells heard by a device have completely aligned or completely disjunct signal spectrums and needs to be addressed accordingly.
Situations similar to those illustrated in FIG. 2 may also arise if one or more of the macro cells has an available bandwidth similar to that of the pico nodes, but only schedules part of it.
Similar situations may also arise if one or more of the macro cells have a larger frequency range than the pico cells and the desired signal is transmitted in a macro cell (see e.g. US2012/0003981A1).
The radio access technology used by the different network nodes (e.g. base stations, pico nodes) to transmit desired and interfering signals may be the same radio access technology for all involved network nodes or may differ between the involved network nodes.
For example, network nodes of different layers of a heterogeneous network deployment may use different radio access technology (e.g. UMTS LTE—Universal Mobile Telecommunication Standard, Long Term Evolution—for the pico layer and UMTS HSPA—Universal Mobile Telecommunication Standard, High Speed Packet Access—for the macro layer or WLAN—Wireless Local Area Network, e.g. according to IEEE 802.11—for the pico layer and UMTS LTE for the macro layer).
Further, the different network nodes that create interference in different regions of the receiving spectrum may use the same or different radio access technologies (even if they are not from different layers of a heterogeneous network deployment). For example, one interfering macro node may use UMTS HSPA and another interfering macro node may use UMTS LTE while the pico node may use UMTS LTE or WLAN, or one interfering pico node may use UMTS HSPA and another interfering pico node may use WLAN while an interfered macro node may use UMTS LTE.
All such examples may experience the above-described situation with diversified (varying, differing) interference within the receiving spectrum.
There is a need for scheduling approaches that perform well in situations with diversified interference within the receiving spectrum.